1. Field of the Invention
The present invention relates to an image process apparatus and an image process method for a panorama/waterglass function. More particularly, the present invention relates to an apparatus and a method for calculating source image coordinates.
2. Description of the Related Art
Conversion between images having different resolutions needs to be performed with care. For example, when a television signal with 4:3 horizontal-to-vertical ratio is applied to a widescreen television with 16:9 horizontal-to-vertical ratio, images are displayed on only a portion of the widescreen while the images maintain the 4:3 ratio, or appropriately scaled images are displayed on the entire 16:9 widescreen. When the images maintain the 4:3 ratio, image distortion does not occur. However, when the images are displayed on the entire 16:9 widescreen, an image distortion problem arises. That is, the image is horizontally lengthened, or broadened, due to conversion of the 4:3 ratio standard television signal to the 16:9 widescreen television signal.
A panoramic function and a waterglass function are provided to solve such problems. The panoramic function, as well as the waterglass function, facilitates a fact that a significant amount of meaningful data of image signals, such as television signals, are generally distributed in the central portion of a screen.
In the panoramic function, while source images with a small horizontal-to-vertical ratio are converted into images with a wide horizontal-to-vertical ratio, the horizontal-to-vertical ratio of the image in the central portion is maintained close to the ratio of the source images, but the horizontal-to-vertical ratio of the image at both sides of the screen gradually increases as the image becomes farther from the center portion of the screen.
In the waterglass function, wile source images with a small horizontal-to-vertical ratio are converted into images with a wide horizontal-to-vertical ratio, the horizontal-to-vertical ratio of the image in the central portion is maintained close to the ratio of the source images, but the horizontal-to-vertical ratio of the image at both sides of the screen gradually decreases as the image becomes farther from the center portion of the screen.
FIGS. 1A to 1C illustrate image conversion concepts, according to a prior art, in which the small horizontal-to-vertical ratio image signals are converted into the wide horizontal-to-vertical ratio image signals. The source images to be converted in FIGS. 1A to 1C are shown as three circles aligned horizontally in FIGS. 1A to 1C.
FIG. 1A is a conceptual view that illustrates converted images displayed on a portion of the screen, when the horizontal-to-vertical ratio is maintained throughout the conversion.
Referring to FIG. 1A, the horizontal-to-vertical ratio is maintained throughout the conversion, so that the images are not displayed on portions of both sides of the screen. Thus, in maintaining the entire screen aspect ratio throughout the conversion, portions of the screen may be wasted.
FIG. 1B is another conceptual view that illustrates the source images converted in proportion to an appropriately scaled aspect ratio corresponding to an output screen.
Referring to FIG. 1B, horizontally widened images with a certain aspect ratio are displayed on the entire screen. The horizontal-to-vertical ratio is altered, so that the images are evenly spread in horizontal.
FIG. 1C is another conceptual view that illustrates an image conversion with the panoramic function.
Referring to FIG. 1C, the images are displayed on the entire screen in a way that maintains shapes of the source images in the central portion of the screen with practically no distortion, but gradually widens the shapes of the source images toward the sides of the screen. Because important portions of images are generally located in the center portion of the screen, distortions in the center portion of the screen are minimized at the cost of large distortions toward the sides of the screen.
FIG. 2 is a graph illustrating a relation between the coordinates of a source image and the coordinates of a converted image in FIG. 1A to FIG. 1C.
The graph in FIG. 2 has a horizontal axis representing a converted image coordinate n after a conversion, and a vertical axis representing an image coordinate x of the source image. A symbol xmax in the vertical axis represents a number equal to a subtraction of one from the number of horizontal pixels of the screen corresponding to the source image, i.e. (the number of horizontal pixels of the screen corresponding to the source image—1). A symbol nmax in the horizontal axis represents another number equal to a subtraction of one from the number of horizontal pixels of the converted screen corresponding to the converted image, i.e. (the number of horizontal pixels of the converted screen corresponding to the converted image—1). In the conversions of FIGS. 1A to 1C, the aspect ratios after the conversions are larger than before the conversions, so that nmax is larger than xmax.
Referring to FIG. 2, the conversion shown in FIG. 1A is represented as a straight line 210 over a portion (from n1 to n2) of the converted image coordinate axis n. The straight line has a relatively steep gradient for maintaining the aspect ratios unaltered throughout the conversion, so that the converted images are displayed on only a portion of the screen.
The conversion shown in FIG. 1B is represented as a straight line 220 with a relatively moderate gradient over the entire converted image coordinates n, for displaying the converted images on the entire screen. The straight line 220 corresponding to the conversion in FIG. 1B has a more moderate gradient than that of the straight line 210 corresponding to the conversion in FIG. 1A, so that the converted images according to the conversion in FIG. 1B are widened.
The conversion shown in FIG. 1C is represented as a curved line 230 that partly has a practically straight line with a rather steep gradient in the center portion of the screen n3 to n4, similar to the conversion in FIG. 1A, and has curved lines with gradually leveling gradients toward the sides, to display the converted images on the entire screen.
A calculation of the source image coordinates is to find a source image coordinate x corresponding to the converted image coordinate n over the graph in FIG. 2. That is, the calculation of the source image coordinates is to find a pixel of the source images from which a pixel of the converted image is converted. The value x may be a non-integer number, and in such cases, through the calculation of the source image coordinates, the pixel of the source images corresponding to an appropriate value x is generated by performing processes such as interpolation.
In the image conversions providing the panoramic function shown in FIG. 1C, the source image coordinates calculation occasionally uses polynomials. In such cases, the calculation with high order polynomials is difficult to implement in hardware, and needs complex hardware such as high-speed multipliers; thus, an implemented hardware may be very complex and expensive.